Since there has been an awareness on the dangers of toxicity, the quick detection of toxic vapors and gases has been a goal set by both equipment users, toxicologist, and government toxic-gas monitoring agencies. These toxic vapors and gases can cause toxicosis, can reduce the quality of the environment and are dangerous to the general health and well being of mankind.
In todays industrial complex and high density vehicular traffic toxic-gas alarm episodes occur more frequently--some are detected but more often than not, they go undetected. Therefore, for the protection of personnel working in potential toxicity areas and the general public, it is necessary that a positive and quick method be available to detect and curtail these toxic gas escapes and prevent a possible catastrophic situation. The toxic detection problem is not limited to enclosed work areas, a leak in an open site, such as a petroleum tank farm or a gasoline service station, could and has led to catastrophic results.
There are several vapor and gas detection devices in use today. However, for the most part, these devices have limitations such as: excessive response time, the necessity of having to be immersed in a fluid, a narrow band of response, extreme thermal sensitivity, hot-wire thermal reaction and unsafe usage in an explosive atmosphere which is especially critical when detecting hydrocarbon emissions.
A search of the prior art did not disclose any patents that read directly on the claims of the instant invention, however, the following U.S. patents were considered related:
______________________________________ U.S. PAT. NO. INVENTOR ISSUED ______________________________________ 3,950,739 Campman 13 April 1976 3,875,499 Roberts 1 April 1975 3,045,198 Dolan etal 17 July 1962 ______________________________________
The Campman patent discloses an apparatus and method for detecting and locating the source of a contaminating gas in a free and unconfined atmosphere. The apparatus includes a semiconductor sensor, whose conductance varies with variations in the density of the gas in the region immediately surrounding the sensor. The sensor is connected to an electronic circuit that produces a voltage that varies with the conductance of the sensor. The voltage output is connected to a pulse generator. As the voltage varies, so does the frequency of the pulses from the pulse generator. The output of the generator, through additional circuits, is connected to visual and audible devices that produce an alarm when a contaminating gas is detected.
The Roberts patent discloses a gas detection system that uses an ionic gas detector to detect leaks in vessels, pipes and other closed systems. The detection is accomplished through the presence of certain tracer gases or vapors which pass into the surrounding atmosphere. These gases or vapors are drawn through a probe into the systems ionic gas detector. The ionic gas detector detects ions from the gas which are induced at a rate which varies with the concentration of the detected gas. The ions are collected at oppositely charged emitter and collector elements. These elements produce a current in an output circuit that is indicative of the concentration of the detected gas.
The Dolan patent discloses a detection circuit that incorporates an electrically operated adsorptive element that is sensitive to the exposure of liquids, vapors or gases. The element, which functions under Van der Walls' adsorption forces, is in a series circuit that includes a meter, a battery and current limiting resistor. Under a normal, no contaminants condition, the meter is adjusted to read zero. When the element is exposed to a contaminating substance, its resistance increases which causes the circuit resistance to also increase and show a change in the meter reading which indicates the presence of a contaminating gas. Reciprocally, when the contaminating gas decreases, the elements resistance decreases causing the circuit resistance to also decrease and return the meter to its zero reading. The element is generally comprised of a base having on its exposed surface a resilient surface with a particle stratum of discrete adsorbent metallic particles. When the element adsorbs a substance a change takes place that increases its resistance.